The present invention relates to a coordinate inputting system; more particularly the present invention relates to a coordinate inputting system which is suitable for being incorporated into a so called digitizer for inputting hand written letters and/or graphics, as for example into a computer system; and even more particularly the present invention relates to a coordinate inputting system, in which each coordinate position of a special pen such as a stylus type pen is inputted, as said special pen touches the surface of a coordinate inputting sheet. This point of contact of the special pen upon the coordinate inputting sheet will hereinafter be referred to as the "input point".
The present inventors wish hereby to attract the attention of the examining authorities to copending patent application Ser. No. 055,946, filed June 1, 1987 which may be considered to be material to the examination of the present patent application.
In the prior art, there have been proposed various types of coordinate inputting systems. One such prior art type coordinate inputting system is illustrated in FIG. 7 of the accompanying drawings in exploded perspective view. In this figure, the reference symbol 1A denotes a X coordinate inputting sheet, which has a resistive surface 4A on its one side and a pair of electrodes 2A and 3A laid along its opposite edges and in contact with opposite edges of said resistive surface 4A And, similarly, the reference symbol 1B denotes a Y coordinate inputting sheet, which has a similar resistive surface 4B on its one side and a similar pair of electrodes 2B and 3B laid along its opposite edges and in contact with opposite edges of said resistive surface 4B. These two X and Y coordinate inputting sheets 1A and 1B are laid together in a mutually parallel relationship with their electrodes 2A, 2B and 3A, 3B extending in a mutually skew perpendicular relationship.
With such a coordinate inputting system, when a tip of a special pen touches the upper or outside surface of the X coordinate inputting sheet 1A and presses on it, while at the same time certain voltages are applied between the electrodes 2A and 3A of the X coordinate inputting sheet 1A and 3A and 3B of the Y coordinate inputting sheet 1B, then divided voltages will be produced respectively from said X coordinate inputting sheet 1A and said Y coordinate inputting sheet 1B as X and Y coordinate information.
There is however a problem with such a coordinate inputting system, in that, when a part of the hand or the arm of the operator, such as his or her wrist or elbow, inadvertently touches the upper or outside surface of the X coordinate inputting sheet 1A and presses on it, then this may produce an erroneous reading from this coordinate inputting system. In such a case, the obtained X and Y coordinate information will be a combination of the positional information generated by the tip of the pen, i.e. the correct and desired positional information, and of the positional information generated by this inadvertent user arm pressure, i.e. incorrect and spurious positional information. In such a case, an erroneous input indication may well be produced.